Build your own laser surveillance system for $20 (or less)
Posted November 15, 2006 
Comments(2) Have you ever seen those laser surveillance systems that allows someone to listen to a conversation remotely through a window? Well, now you can build one yourself, and for less than $20!
Found across the internet, companies sell so-called “spy gear” to be able to listen to conversations from as far away as a mile away. Well, now you can build one yourself!
The principle behind this seemingly impossible technology is simple. During a conversation, the sound waves from the speaker move throughout the room. As the sound waves strike a glass window, a VERY small vibration is introduced and can be used to your advantage. Utilizing a visible light laser (or infrared for secrecy), you can “carry” the vibration via a laser light to a phototransistor which is fed into preamp and amplifier. You can substitute the preamp/amplifier set up with a laptop that has a microphone port.
Some tips to remember:
1. Use a sheet of cardboard or white paper to find the reflected laser beam when setting up or calibrating. This is assuming you do not want to be secretive about your little adventure or you are perfecting you setup for the first time.
2. Use an infrared laser if you don’t want the target to pick up on your scheme. I strongly suggest that you be sure to respect any laws in your area of the world concerning surveillance of this type. Don’t say I didn’t warn you!
So how do you build this, you ask? As always, links are at the bottom of the article. Have fun and good luck!
Links:
http://www.electromax.com/laser.html <--- To see an example commercial system
http://www.instructables.com/id/EF9RFCKV9JEPORT41Y/ <— The instructions to build the device.